Self-biasing percussion system for an electronic organ

ABSTRACT

A self-biasing percussive gate for an electronic organ including a relatively small capacitor C1 in series with a continuously connected tone signal source which provides positive signal pulse trains of selective frequencies, in response to playing of the organ, the small capacitor C1 being connected in a shunt path to ground which contains a first diode and a large capacitor C2, the first diode being poled to conduct in response to positive signal. The anode of the first diode is connected to the cathode of a gating diode, the anode of which is connected to a load circuit. A timing circuit is provided between the source and the small capacitor to smooth and control voltage changes during each pulse. Means are provided for momentarily short circuiting the large capacitor, as each tone is called for by the player, an action which initiates the percussive tones. Each tone persists for a time which is inversely proportional to the frequency of that tone signal, and has a progressive modification of tone color in proceeding from its initial to its final points. Tone color is also a function of frequency.

United States Patent Inventor David A. Bunger Cincinnati, Ohio Appl. No. 782,367

Filed Dec. 9, 1968 Patented Feb. 23, 1971 Assignee D. H. Baldwin Company Cincinnati, Ohio SELF-BIASING PERCUSSION SYSTEM FOR AN ELECTRONIC ORGAN 12 Claims, 3 Drawing Figs.

Primary Examiner-W. E. Ray Assistant Examiner-Stanley J. Witkowski Attorneys-W. H. Breunig and Hurvitz, Rose & Greene ABSTRACT: A self-biasing percussive gate for an electronic organ including a relatively small capacitor C 1 in series with a continuously connected tone signal source which provides positive signal pulse trains of selective frequencies, in response to playing of the organ, the small capacitor C being connected in a shunt path to ground which contains a first diode and a large capacitor C the first diode being poled to conduct in response to positive signal. The anode of the first diode is connected to the cathode of a gating diode, the anode of which is connected to a load circuit. A timing circuit is provided between the source and the small capacitor to smooth and control voltage changes during each pulse. Means are provided for momentarily short circuiting the large capacitor, as each tone is called for by the player, an action which initiates the percussive tones. Each tone persists for a time which is inversely proportional to the frequency of that tone signal, and has a progressive modification of tone color in proceeding from its initial to its final points. Tone color is also a function of frequency.

FILTER? 1? BACKGROUND OF THE INVENTION the frequency of the input tone signal and in which tone color changes during the wave.

Percussive circuits are employed in electronic musical instruments in order to simulate, as closely as possible, percussive sounds produced by certain conventional musical instruments, for example, stringed instruments. Percussive circuits of the electronic type generally provide a percussive toneof predetermined fixed duration irrespective of the fundamental frequency of the input tone applied to the circuit. However, the fixed duration of the percussive tone represents a departure from realistic simulation of percussive tones produced by some conventional musical instruments, for example, the more taut a vibrating string, the higher willjbe its fundamental frequency of vibration and the shorter will be its damping period, when it is plucked or picked. A percussive circuit should provide tones which conform with this characteristic.

Prior art percussive gates have been controlled in terms of controllable gating bias voltages. It is desireable to eliminate bias voltages, in order to reduce circuit complexity. It is therefore another object of the present invention to provide a selfbiased percussive gating circuit which is operative from an input tone signal to maintain the gate inhibited and to control theconductivity of the gate during each output tone.

Another aspect of tone simulation with which the present invention is concerned is production of a variation is tone color, which is characteristic of percussive tones in conventional instruments. Considering the vibrating string again, for

example, the modes of vibration may vary as the percussive or damped tone amplitude becomes smaller, or as a function of pitch.

It is another object of the present invention to provide a percussive gating circuit for providing a percussive output tone in which tone color varies as a function of time, or as a function of the instantaneous amplitude of the tone signal.

It is still anotherobject of the present invention to provide a self-biased'percussive gating circuit for providing a percussive output tone having a duration which varies inversely with fundamental frequency of the tone signal and wherein tone quality varies with tone signal amplitude.

SUMMARY OF THE INVENTION A percussive gate providing a wave shape having a duration inversely proportional to the frequency of an input tone signal, and having a gradually changing tone color as the wave shape proceeds in time. The gate is normally biased off in response to the tone signal, and each percussive wave shape is initiated by transiently grounding a control point of the gate. So long as the control point remains grounded, the gate is conductive. When the control point is released, the gate becomes progressively less conductive, until turn-off, in increments each of which is provided by a cycle of the tone signal;

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a percussive gate circuit according tothe present invention;

FIG. 2 illustrates plots of signal waveforms appearing at specified locations in the circuit of FIG. 1 during typical operation of the circuit,

FIG. 3 shows wave shapes of typical input signals, produced as an organ is played. 9

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The action of the gate of the invention commences with short circuiting of capacitor C and release of the short circuit. The first pulse to arrive after release of the short circuit drives current in the circuit R,C.,, which has a time constant much smaller than pulse duration. Point A, rises exponentially to the full pulse amplitude, say 10. v., and the voltage at point A, is transferred, while it is increasing, to the point B through capacitor C,, i.e., VA, VB, since no current flows in C,. The potential at point B therefore rises exponentially, following the potential at point A, until about .6 v. is attained by point B, at which time diode D becomes conductive. Capacitor C, now accepts charge, but its capacitance is so great relative to the capacitance of C, that the current which can flow to it via C, is incapable of raising its voltage by more than a very small increment. C therefore acts as a clamp, for the duration of the positive pulse, for point B. During the process above described D is nonconductive, which isolates the load resistance R The net voltage across C, is then 10. v. .6 v. 9.4 v.

When the input pulse proceeds negatively, the capacitor C, discharges exponentially. Point B, which initially was nearly at the voltage of C i.e., about .6 v., attempts to follow the voltageof point A, to which it is coupled. Point A,,moves from 10. v. back to a reference level, say 0. v., which requires that point B fall by 10. v. The fall of the left side of C,, is the same as the fall of point A,, i.e., is exponential. Point B follows point A, until point B becomes negative by .6 v. At that time, current flows in R through D, and into C, attempting to bring the voltage across C, to zero. However, the apparent impedance of C, is quite small only while point A, is rapidly varying. As C, attains the slowly varying portion of its exponential decay, the total current passed by C, reaches a maximum and then commences to decay toward zero. This is explained best by reference to the formula ICE For

de -O we have a zero flow of current into a capacitor. The current into C, is then a function of the rate at which the voltage across C is changing, as well as of the value of R,,, which together with the capacitance of C, provides a time constant. The current through the load thus builds to a maximum and then begins to decrease back towards zero, as the rate of change of voltage across C, decreases toward zero. Before current can quite decrease to zero, the next positive pulse arrives. The voltage of A, commences a second exponential rise.

The voltage of the point B now initially follows the voltage at A, because no current initially flows into C,. The rise continues until the stored voltage of C is exceeded by .6 v., that differential being requiredto turn on diode D At that time current flows into C,, but C, being a very large capacitor, its voltage rises by only a very small increment. The voltage at B is now increased slightly. If it were 1.2 v., the voltage across C, would be 8.8 v. i.e., the voltage across C, is equal to the input pulse peak voltage less the voltage at B. When the second pulse goes negative and the voltage of point A, follows exponentially, the voltage across C, remains constant, i.e., both plates of the capacitor fall in voltage until point B goes sufficiently negative, i.e., falls more than 8.8 v. At this time, current flows from ground up through R, and through diode D to capacitor C,. The voltage at B now is a function of current in R But this current is a function of the rate at which the voltage of A, varies and as this rate slows, the current attains a peak and thereafter decreases toward zero. This decrease is terminated abruptly by arrival of a third positive pulse.

The sequence proceeds, with C 'increasing its voltage in increments, until C attains a voltage which equals the peak-topeak voltage of the input signal. In this condition the gate is rendered nonconductive.

The system requires that C, be larger than C,. Rate. of rise and fall of voltage at A, is then almost wholly a function of the time constant R,C,. I

Connected across C, is an NPN transistor T,, having its emitter grounded. T, is normally maintained nonconductive, during generation of a permissive tone signal wave, but is rendered transiently conductive to initiate the percussive tone signal wave,'for the purpose of transiently shorting C The circuitry which controls T, is as follows. A tone signal input is applied to terminal Y, on actuation of any pedal of an electronic organ. The tone signal is coupled through C,, and diode D, to charge capacitor C A large resistance R, is connected between the anode of D, and ground, so that C,, tends to remain charged and to block D, on tone pulses following the first of a series. A small current-limiting resistance R,, is connected between the cathode of D, and the base of T,. R, provides a return path for the cathode of D, and R a DC connection from the base of T, to ground, which normally maintains T, nonconductive.

In FIG. 3 is illustrated atypical time cycle of pedal actuation. Different pedals may be actuated in sequence, or the same pedal may be actuated repeatedly. In any event, pedal actuations L, M, N, are time separated, as'O, P, 0. Tone signal is applied to point Y whenever any pedalis actuated, but the frequency of this signal is a function of pedal selection, and therefore generally varies in normal playing of the organ.

Signal at point X is at the same frequency as signal at point Y, but each signal at X endures until a succeeding signal appears. Thus, on depression of pedal 01., point Y sees signal R at frequency F, for as long as pedal -12 is actuated, but point X sees signal of frequency f, for the time L O, i.e. until pedal 02 is actuated. This action is produced by what is known as a latch circuit, and the particular latch'cir cuit employed in the practice of the present invention is thatdisclosed in application for U.S. Pat. Ser. No. 683,689 filed Nov. 16, 1967, in the name of Munch & Uetrecht, assigned to the assignee of this application, and entitled Electronic Latch and Wipeout System. I

On arrival of a signal train at point y, D conducts the first pulse to arrive. This pulse turns on T,,- and also stores a charge in C, and in C,,. The charge in C decays rapidly, permitting T, to become nonconductive. The charge in C,, maintains D, nonconductive, so that succeeding pulses cannot turn T, on. It follows that T, is turned on by the first pulse. of a train to arrive, and in the interim between trains restores in preparation for arrival of the next train.

The anode of D is directly connected to the cathode of D.,. Resistances R R, are connected from the anode of D, to ground and a resistance R, is connected by capacitor C to the junction of R R,,. A tab switch T is connected to the signal side of R and the switch leads to amplifier Am and loudspeaker Sp. R R R-,, C, constitute an RC tone color filter, but also provide a path from ground through D, and D a to point B. D, supplements D, in providing isolation in response to positive voltage at point B, but in theory, is not required.

The present invention provides percussive tones which have durations which are inverse functions of the input tone signal frequency. This is true because C, requires approximately equal charge increments per pulse regardless of pulse frequency; acquiring most of this chargeat the instant that D becomes conductive. A higher pulse input frequency will therefore drive point B to cut off in a shorter time than will a lower pulse input frequency. I

At the same time, the wave shapes of successive pulses constituting a percussive train of pulses varies, not alone in respect to amplitude, but successively occurring pulses tend to flatten increasingly. Wave-shap variations are equivalent to frequency spectrum variations or tone color variations so that as each percussive train develops, the sound of the tonal output of loudspeaker Sp progressively changes. The two effects described, i.e., modification of percussive train durations as a function of frequency and modification'of tone color in the course of each wave train, are interrelated so that highpitched tones are not of the same character as low-pitched tones. The effects serve to stimulate the percussive tones provided, for example, by plucked strings, more accurately than has been the case hitherto.

The input wave form may have a zero base line, as was assumed in the above discussion. Should the wave form have a nonzero base line, the theory of operation of the system is not essentially modified because the DC component of the signal finds no conductive path, but provides a division of steady state charges on the capacitance of the system, e.g., C,, C,, C,,. Reference is made to FIG. 2, illustrating certain wave shapes useful in explaining the invention. The input wave form goes from +2. v. to +10. v. The voltage at point B is plotted under the designation B, on dotted lines. Parts E of curve B represent the clamping action of C, and curve F indicates how part B would move in voltage in absence of clamping action. Full line D represents the voltage across the load, and constitutes the output signal. 1

The point X of FIG. I of the accompanying drawings may be connected to points 39 or 39A of FIG. 1 of Ser. No. 683,689, and the point Y may be connected to the collector of T However, the present invention, while utilizable in conjunction with the circuit of Ser. No. 683,689, as one possible utility, is not restricted to such utility. Other forms of latch circuits may be employed, or percussive control pulses may be derived in other ways than by means of latch circuits, for transiently turning on T on initiation of a percussive tone. Generally speaking, it is conventional to provide control pulses on actuation of keys or pedals for the purpose of initiating percussive tones, and such pulses may be generally employed in initiating cycles of operation of the system.

The wave form of H6. 2 typifies the actual wave form occurring in operation of the system of FIG, 1, but in fact perhaps 50 pulses would occur per percussive wave. FIG. 2 exaggerates the difference betweensuccessive output pulses. Nevertheless, by proper choice of time constants and relative values of C, and C,, any desired number of pulses per percussive wave can be caused to occur, and the output wave shapes per pulse can be widely modified.

For purpose of analyzing the circuit, it can be assumed that a resistance extends from X to ground, or a reference point slightly above ground, and another from Y. These resistances are included in one side of a multivibrator divider stage, and provide conductive paths from X, Y to ground.

Iclaim: i

1. A percussive gating system, comprising:

a source of tone signals in the form of discrete pulses;

a load circuit;

a diode gate connected between said source and said load circuit",

means normally maintaining said diode gate fully inhibited to said pulses; and

means inclusive of said last means and responsive to a control pulse for controlling said diode gate gradually over a time period from a fully uninhibited condition at the time of said control pulse to a fully inhibited condition following termination of said control pulse in increments each responsive to one of said discrete pulses.

2. The combination according to claim I, wherein said last means includes a capacitive counter responsive to said discrete pulses.

3. The combination according to claim 2, wherein said capacitive counter includes a relatively small capacitor in series with said source, and a diode and a relatively large storage capacitor in series with said relatively small capacitor, said diode being poled to charge said storage capacitor in response to each of said discrete pulses, said storage capacitor being unbypassed.

4. The combination according to claim 3, wherein is provided a further diode connected between said load circuit and said relatively small capacitor, said further diode being poled to block said discrete pulses, but to pass discharges of said relatively small capacitor to said load circuit.

5. A percussive gate, comprising:

a source of discrete pulses of only one polarity;

a gate normally inhibited for said pulses;

means for developing a control voltage proportional in amplitude to the number of said pulses occurring after a control signal in response to said discrete pulses;

means for developing load current pulses via said gate only in response to falls of said pulses; and

means for controlling the amplitudes of said load current pulses as a direct function of the amplitude of said control voltage by controlling said gate.

6. In a percussive gate, a source of discrete pulses:

a load circuit, a first diode connected in series with said load circuit and poled to inhibit said discrete pulses from driving current into said load circuit; and

a timing resistance and a first and a second capacitor connected in series with said'source,'-said second capacitor having at least thirty times; the capacitance said first capacitor, a second diode connected between said capacitors, said diode being poled to pass current to said second capacitor in response to said pulses, and means for discharge of said first capacitor through said load circuit via said first diode in response to each of said pulses.

7. In an electronic organ: I

a source of tone signal pulses,

a capacitor;

means responsive to occurrence of successive ones of said pulses for charging said capacitor to progressively smaller voltages; V

a load circuit; and t means responsive to cessation of: each of said tone signal pulses for discharging said; capacitor through said load circuit.

8. The combination according to claim 7, wherein said means responsive to occurrence of successive ones of said pulses includes a storage capacitor, means responsive to successive ones of said pulses for adding increments of charge to said storage capacitor, and means for offsetting the voltages of said pulses with the voltages across said storage capacitor in charging the first mentioned capacitor.

9. In an electronic organ: a load circuit; means providing tone signal pulse trains which endure for at least the times of key actuation; I means responsive to only the first pulse of each of said trains for initiating a gating operation; and

means responsive to said initiationfor transferring a percussive wave train at the frequency of said tone signal pulses to said load circuit.

10. A percussive gate for an electronic organ, comprising:

a source of discrete tone pulses of only one polarity and of uniform amplitude;

a gate normally inhibited for said pulses and including a diode poled to inhibit said pulses and a capacitor in series with said diode;

means for generating a wave train initiating pulse;

means providing a source of monotonically increasing voltage of the same polarity as said pulses commencing with said inhibiting pulse;

means applying said monotonically increasing voltage to the junction between said capacitor and'said diode; and

a resistive load circuit connected in cascade with said diode.

l l. A percussive gate for an electronic organ, comprising:

a source of alternating signals;

a timing resistance;

a first capacitor;

means connecting said source, said timing resistance and said first capacitor in a series circuit;

a second capacitor;

a first diode;

a load; 1

means connecting said second capacitor, said first diode and said load in a series circuit across said first capacitor; and

a second diode and a third storage capacitor connected in the order named in series with each other from the junction of said second capacitor and said first diode to a point of reference potential, said first and second diodes being oppositely poled as seen from said junction.

12. A percussive gate for an electronic organ, comprising:

a source of pulses of first polarity with respect to the potential of a reference path;

a first relatively small capacitor;

a first diode; 1

a load resistance;

means connecting said source, said first capacitor, said diode and said load resistance in a series circuit, said diode being poled to inhibit said pulses;

a timing circuit connected between the junction of said first capacitor and said reference path; and

said timing circuit including a second diode and a second relatively large capacitor, said second diode being poled to pass said pulses. 

1. A percussive gating system, comprising: a source of tone signals in the form of discrete pulses; a load circuit; a diode gate connected between said source and said load circuit; means normally maintaining said diode gate fully inhibited to said pulses; and means inclusive of said last means and responsive to a control pulse for controlling said diode gate gradually over a time period from a fully uninhibited condition at the time of said control pulse to a fully inhibited condition following termination of said control pulse in increments each responsive to one of said discrete pulses.
 2. The combination according to claim 1, wherein said last means includes a capacitive counter responsive to said discrete pulses.
 3. The combination according to claim 2, wherein said capacitive counter includes a relatively small capacitor in series with said source, and a diode and a relatively large storage capacitor in series with said relatively small capacitor, said diode being poled to charge said storage capacitor in response to each of said discrete pulses, said storage capacitor being unbypassed.
 4. The combination according to claim 3, wherein is provided a further diode connected between said load circuit and said relatively small capacitor, said further diode being poled to block said discrete pulses, but to pass discharges of said relatively small capacitor to said load circuit.
 5. A percussive gate, comprising: a source of discrete pulses of only one polarity; a gate normally inhibited for said pulses; means for developing a control voltage proportional in amplitude to the number of said pulses occurring after a control signal in response to said discrete pulses; means for developing load current pulses via said gate only in response to falls of said pulses; and means for controlling the amplitudes of said load current pulses as a direct function of the amplitude of said control voltage by controlling said gate.
 6. In a percussive gate, a source of discrete pulses: a load circuit, a first diode connected in series with said load circuit and poled to inhibit said discrete pulses from driving current into said load circuit; and a timing resistance and a first and a second capacitor connected in series with said source, said second capacitor having at least thirty times the capacitance said first capacitor, a second diode connected between said capacitors, said diode being poled to pass current to said second capacitor in response to said pulses, and means for discharge of said first capacitor through said load circuit via said first diode in response to each of said pulses.
 7. In an electronic organ: a source of tone signal pulses, a capacitor; means responsive to occurrence of successive ones of said pulses for charging said capacItor to progressively smaller voltages; a load circuit; and means responsive to cessation of each of said tone signal pulses for discharging said capacitor through said load circuit.
 8. The combination according to claim 7, wherein said means responsive to occurrence of successive ones of said pulses includes a storage capacitor, means responsive to successive ones of said pulses for adding increments of charge to said storage capacitor, and means for offsetting the voltages of said pulses with the voltages across said storage capacitor in charging the first mentioned capacitor.
 9. In an electronic organ: a load circuit; means providing tone signal pulse trains which endure for at least the times of key actuation; means responsive to only the first pulse of each of said trains for initiating a gating operation; and means responsive to said initiation for transferring a percussive wave train at the frequency of said tone signal pulses to said load circuit.
 10. A percussive gate for an electronic organ, comprising: a source of discrete tone pulses of only one polarity and of uniform amplitude; a gate normally inhibited for said pulses and including a diode poled to inhibit said pulses and a capacitor in series with said diode; means for generating a wave train initiating pulse; means providing a source of monotonically increasing voltage of the same polarity as said pulses commencing with said inhibiting pulse; means applying said monotonically increasing voltage to the junction between said capacitor and said diode; and a resistive load circuit connected in cascade with said diode.
 11. A percussive gate for an electronic organ, comprising: a source of alternating signals; a timing resistance; a first capacitor; means connecting said source, said timing resistance and said first capacitor in a series circuit; a second capacitor; a first diode; a load; means connecting said second capacitor, said first diode and said load in a series circuit across said first capacitor; and a second diode and a third storage capacitor connected in the order named in series with each other from the junction of said second capacitor and said first diode to a point of reference potential, said first and second diodes being oppositely poled as seen from said junction.
 12. A percussive gate for an electronic organ, comprising: a source of pulses of first polarity with respect to the potential of a reference path; a first relatively small capacitor; a first diode; a load resistance; means connecting said source, said first capacitor, said diode and said load resistance in a series circuit, said diode being poled to inhibit said pulses; a timing circuit connected between the junction of said first capacitor and said reference path; and said timing circuit including a second diode and a second relatively large capacitor, said second diode being poled to pass said pulses. 